These were senior kendo instructors performing Nihon Kendo Kata (two man prearranged sword forms)
There are 7 for the katana and 3 for the shoto.
Notice the Kendo students seated watching.
These were developed to teach advanced kendo students the realities of a real sword as opposed the shinai they use in kendo.
This is the intensity of concentration that should always be exhibited when professionals are training.
In an older traditional ryu, they probably would have followed up with a strike with the tsuka (tsuka ate)and possible disarm (tachidori)
So you would not probably be able to tell if there really was an accident here or not part of the performance.
Notice how the senior instructor with the katana, knees must have been bothering him, as he had a hard time with the reiho (ceremonial form) at the beginning of the set.
This shows that in reality, anything can happen. (and usually does)
The jutte (iron truncheon) would be used to strike swords at this junction also, with the same effect.